RESUMEN
The Ili River Valley in Xinjiang, China, is a typical seasonal frozen area where loess landslide disasters have become increasingly common during the freeze-thaw periods in recent years. This study analyzed the macroscopic mechanical strength and microstructure changes of the Ili loess under different freeze-thaw cycles (FTCs) through the post-freeze-thaw triaxial compression test on the unsaturated soil in laboratory. Apart from the scanning electron microscopy (SEM), and the nuclear magnetic resonance (NMR), the macro-micro correlation analysis and the cluster-principal component analysis were applied for the theoretical discussion. The results indicated that the cohesive force of the loess exhibits an initial decreases, followed by the increases, and eventually keep stable after various FTCs, while the internal friction angle showed the opposite developing trend before the final constant. Similar to the strong correlation between the cohesive force and the particle abundance, the internal friction angle is also closely related to the abundance and orientation fractal dimension of the loess particles. However, the principal component analysis results showed that cohesive force strongly correlates with the average maximum pore size and the pore size fractal dimension, for which the internal friction angle most strongly affected by the average maximum particle size. The possible reason is that the extracted principal components represent a class of microscopic parameters with the same or similar change trend, although there may be a certain offset between them. The mechanical deterioration of loess is attributed to the repeated frost heaving force and the migration potential caused by FTCs. The alterations of the microstructure accelerated the deterioration of the macroscopic mechanical properties of the loess, which further widens the understanding of the mechanism behind the deterioration of loess mechanical strength in the Ili River Valley under FTCs, and contributes to the prevention and management of the local landslide disasters.
RESUMEN
This paper presents an experimental investigation on the propagation of chemical grouting in a two-dimensional permeated fracture network with various aperture widths. As grouting engineering is often concealed in most experiments, the propagation of grout in fractures is not fully understood. The anisotropic permeability of geological masses with different aperture widths was found and has been investigated since 1960. The deflection flow effect was first found by Tian for groundwater flow in two groups of fractures with different aperture widths. Field grouting indicated that the grout propagates along a group of fractures with larger apertures that are longer while propagating a shorter distance along fractures with small apertures. This phenomenon implies a deflection for grout propagation in fractures with different aperture widths. The results of our study confirm this and indicate that there would be an anisotropy of grout propagation when the two groups of aperture widths are different. The water flow conditions also cause the difference in grout propagation length. When the aperture widths of the two groups of fractures are the same, the propagation shows symmetrical ellipse propagation. The results show the anisotropy of the grout increases as the aperture width ratio increases. This study helps in understanding the mechanism of chemical grouting in fractures with different apertures and flowing water and outlines some implications for grouting design in a fractured rock mass.
RESUMEN
In this study, we document several experiments that investigate the speed of the flow of fine sand through a fixed porous bed of packed glass beads under various conditions, including the height of the sand column (H) and porous bed (h) and the diameter of the glass beads (D) and sand grains (d). The experiments are conducted with glass beads packed at a constant density and sand at a different dry bulk density. The results show that the height of the sand does not affect the speed of the sand flow. The speed of the sand flow (v) decreases with an increase in h until h approaches a certain value. An equation [Formula: see text] is proposed, where a and k are the experimentally determined coefficients. Moreover, the flow of sand through a fixed porous bed could be regarded as parallel flow through multiple pipes, and therefore, the relationship between D and the number and diameter of pipes, N and D p, are discussed. Further investigations are needed for the result that the flow of sand through a porous bed or multiple parallel pipes cannot be simplified to flow through one orifice with a certain diameter.